Aspects of the ecology of gulls in the urban environment
A survey in 1994 recorded nearly 14,000 pairs of Larus gulls of four species nesting on buildings in Britain and Ireland. The majority of these records involved Herring Gulls, although large numbers of Lesser Black-backed Gulls were also observed. Since the last such survey in 1976, Lesser Black-backed Gulls had shown the highest rate of increase. Despite the sharp decline in the numbers of Herring Gulls breeding in Britain and Ireland since the mid-1970s, numbers nesting on roofs had continued increasing, albeit at a lower rate than before. New developments since 1976 included increasing numbers nesting inland and on the roofs of large industrial buildings. The study of a colony of Herring Gulls and Lesser Black-backed Gulls nesting on one such industrial building showed that the breeding success of these birds, although lower than that found for roof-nesting birds at more dispersed colonies, was higher than that at many traditional colonies. Low nest density, shelter for chicks and safety from predators were thought to be important contributors to this success. In addition, die colony was situated very close to the sources of food, agricultural land and urban areas, found to be most important in die diet of Herring Gulls nesting there. A review of dietary studies of roof-nesting Herring Gulls found that, despite the location of such colonies in urban areas, urban sites were not always an important source of food. The reduction in availability of one urban source of food, untreated sewage, was found to have little effect upon the gulls using an urban stretch of river. In particular, neither of the species causing most problems in urban areas, the Herring Gull and Lesser Black- backed Gull, decreased in number; in fact, numbers of these species nesting on buildings in the area increased considerably.